The present invention relates to an apparatus for cleaning grits of the type having a plurality of superimposed screen layers, means for vibrating the screen layers, an air circulation through the screen layers, and collecting means for providing the screen discharge at an outlet of the apparatus.
Apparatus of the aforementioned type for cleaning grits, constitute special machines which are almost exclusively used in flour milling. They make it possible to sort, from the product supplied to the machine, grits and dust and individual corn grits.
The main function is the sorting of the grits fractions with a maximum granulation range and consisting of clean grits, mixed products, light products, special products (cooking grits, etc.), seed, etc. The maximum yield of clean grits is sought.
Fluctuations in the incoming capacity of the product must not have a negative influence on the working quality. The machine setting must not be unintentionally changed during the working process.
On the basis of the principles of industrial processing engineering, it would be conceivable to obtain the components through a number of different separation systems. The main criteria are the heaviness of the fractions, the sinking speed of the fractions in the air flow and the size of the fractions.
Other branches of industrial processing engineering use for such tasks, e.g. fluidized beds with pulsating air, centrifugal sifters, tare means, air classifiers and other equipment. However, it has been found that such equipment cannot be used for improving the grits cleaning machine. The specific demands made in connection with the obtaining of grits can clearly only be met with the known grits cleaning machines known since the beginning of the 18th century. It has been once again found that, as in many other long known technical solutions, such as the bicycle, it is extremely difficult to find important new ideas and convert them into practice.
The known grits cleaning machines have in the meantime been constructionally and functionally developed (and have also required certain framework conditions) in such a way that the Experts could not have expected further significant improvements, particularly with regards to overall design.
The problem of the present invention is to develop a grits cleaning machine, which compared with known machines of this type, in particular permits a further improvement in the production rate, facilitates the cleaning thereof, has lower power requirements and allows particularly inexpensive manufacture, without reducing the quality and yield of the end products.
According to the invention this problem is surprisingly solved in connection with an apparatus for cleaning grits of the aforementioned type, in that the apparatus is constructed as a stand with a stand top, a stand base and a vertical intermediate support interconnecting said top and base, the screen layers being constructed as dust boxes, whilst being supported in vibratable manner in the vicinity of the stand base, the stand top being formed by the upper air distribution chamber. The novel solution firstly provides free space for the central operating functions, whilst auxiliary functions are concentrated at non-disturbing points. The solution according to the invention makes it particularly simple to keep the apparatus clean, as well as the area around the apparatus. Initial tests revealed that this solution as a whole leads to advantages, without any disadvantages being apparent. In addition, the invention makes it possible to realize a number of unexpected improvements in connection with the further particularly advantageous developments, which will be referred to hereinafter.
Preferably in the case of a grits cleaning machine according to the invention, constructed in the form of a double machine, the stand is provided with an intermediate support at either end. The dust box can be supported in vibratable manner by means of a spring system, e.g. on a base structure of the stand. As the actual core of the machine, the dust box is preferably supported in the vicinity of the stand base and the space above it is utilized for the optimum construction of the upper air distribution chamber. The invention permits a clean circulation of the product, as well as an optimum distribution of the air. Through supporting the vibration mass at the bottom, preferably at the stand base, the vibration forces are directly led off. The stand can be designed for its main function of carrying the various components. Due to the fact that both the cleaning of the grits and the necessary mechanical forces are concentrated on their actual working zone, not only can the work quality be maintained and the productive efficiency increased, but also the life of the complete apparatus can be increased. The vibration forces can be kept completely away from the air circulating components, so that once the air circulation has been set or the flaps are correspondingly positioned, there can be no further undesired self-adjustment.
A resilient component is preferably positioned between the stand and the dust box, so that the reaction forces on the apparatus, which result from the vibration forces, can "peter out" in the actual apparatus, because the stand and the stand top represent an effective counterweight with respect to the vibrating components. According to another preferred embodiment, the elastic member can be positioned between the stand base and the intermediate support of the stand. According to another preferred development of the invention, the elastic members are arranged between the intermediate support of the stand and the stand top. Preferably, the intermediate supports themselves are constructed as elastic components, so that an unexpectedly quiet stable operation of the apparatus is obtained.
According to a further preferred embodiment of the apparatus according to the invention, the intermediate supports project over the dust box at the top and at the bottom pass symmetrically and at both ends into in each case a stand base, the space between the two stand bases being free from immovably fitted components. Thus, over and beyond the length of the complete apparatus, there is lateral space for air circulation, also on the inside thereof.
An unexpectedly favourable influence both on the air circulation and on the separation of the end products can be obtained in that below the dust box for the air intake is formed a lower air distribution chamber by means of a discharge which is supported at the bottom in vibrating manner and preferably between the discharge base and the dust box air intake gaps of roughly a few centimeters are formed.
It has hitherto been assumed in the case of apparatuses operating in suction manner, that the air intake zone below the fluidized bed was not particularly problematical, local problems in the incident flow having no significant influence on the air distribution. Only as a result of the present invention was it recognized that hitherto a definite source of problems had been overlooked in the lower air distribution chamber, because in the known constructions, said chamber was simultaneously also used for the purpose of distributing the individual end product fractions. As it was assumed that the individual fractions would in any case drop downwards as screenings, no further attention was paid to this point prior to the present invention. The solution according to the invention provides a clearly defined lower air distribution chamber and the supply of the individual fractions can take place below said chamber, whilst being separated by the discharge base. Generally two to four different fractions are obtained from the screenings, the granulation varying in the longitudinal direction. In order to ensure a maximum clear separation into the indivudal fractions, according to a further advantageous embodiment of the invention, the discharge base is constructed as an inwardly sloping conveyor chute having a plurality of product guide flaps in its central lower portion.
If two collecting devices constructed as double conveyor chutes are arranged below the base and which in each case have two different outlets in the longitudinal direction, advantageously a particularly sharp separation into the desired fractions can be obtained in that the bottom has individual trough-shaped depressions corresponding to the number of product guide flaps and the lower opening of said depressions can be emptied, as required, to either of the collecting devices by means of the product guide flaps. The product guide flaps as chutes tiltable about a pivot point in each case are preferably constructed in such a way that the cross-section of the outlet between the chutes and the discharge base is smaller than the cross-section of the air intake gaps. As the air flow seeks the path of least resistance, a corresponding air flow is ensured by the indicated solution, so that the product removal area remains free from any disturbing air flow. As stated, it is possible to arrange directly above the stand base, a double conveyor chute vibrating in the same direction as the dust box and which is supported on the stand base, whereby preferably a vibrating movement is selected for the same, which differs from the vibrating movement of the dust box.
Another advantageous development of the invention comprises, viewed in the air flow direction, the adjusting flaps being positioned behind the air distribution chamber. According to another advantageous development of the invention, over the screen layers, the air distribution chamber has a conically tapering shape with a plurality of bulkhead-like air circulating chambers, which extend close to the uppermost screen layer, an ajusting clap being arranged in each case in a transition piece between the upper end of the tapered shape of the air circulating chambers and the suction channel. The transition piece preferably runs between the upper end of the tapered shape of the air circulating chamber and the suction collection channel, in a substantially horizontal manner. Preferably the said channel is mounted as a separate component on the air distribution chamber and has a cyclone-like construction.
Appropriately, the dust box and the discharge base are constructed, according to an advantageous development of the invention, as a vibrating standard unit and the two ends are supported at the bottom in vibrating manner, preferably on the stand base. It is also advantageous if the dust box and double vibrating conveyor chute are driven by a common unbalance exciter, the dust box preferably being fixed to the latter and its force action direction is adjustable. Advantageously for increasing the vibrating travel, the double vibrating conveyor chute can be driven by means of a lever joint by the vibratable unit, in that by means of an end support the collecting means is oscillated from the dust box by an actuating lever and support. The articulation points of the lever on the end support, as well as on the collecting means support being variable for adjusting the range.
According to a particularly advantageous development of the invention, the dust box is supported by means of a spring system, so that the complete vibrating structure is given two additional "degrees of freedom" for the vibrating movement. The spring system preferably has hollow rubber springs, steel springs or a flexible rubber coupling. This makes it possible to fix the vibration exciter to the dust box, whilst still making the force action direction adjustable. As a function of the force action direction with respect to the centre of gravity of the vibrating unit, it is possible to adjust the vibration at the beginning and end of the dustbox in both direction and intensity, as required. When supporting the collecting means via a vibratable lever system, which is preferably vibratable by an adjustable actuating lever from the dustbox, the vibration amplitude can be chosen independently of the vibrating movement of the dust box, although this takes place with the same unbalance exciter .